<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <title>01_box-sizing</title>
    <style>
        .box1 {
            width: 200px;
            height: 200px;
            background-color: deepskyblue;
            padding: 5px;
            border: 5px solid black;
            margin-bottom: 20px;
            /*content-box 默认值*/
            box-sizing: content-box;
        }
        .box2 {
            width: 200px;
            height: 200px;
            background-color: gray;
            padding: 5px;
            border: 5px solid black;
            box-sizing: border-box;
        }
    </style>
</head>
<body>
    <div class="box1"></div>
    <div class="box2"></div>
</body>
</html>